Superconductivity With And Without Glue And The Role Of The Double-Occupancy Forbidding Constraint In The T-J-V Model

The occurrence of retarded (with glue) and unretarded (without glue) pairing is thoroughly discussed in cuprates. We analyze some aspects of this problem in the context of the t-J-V model in a large-N approximation. When 1/N renormalizations are neglected the mean-field result is recovered, where the unretarded d-wave superconducting pairing triggered by the spin-exchange interaction J is obtained. However, the presence of a nonnegligible nearest-neighbors Coulomb interaction V (q) kills superconductivity. If the non-double-occupancy constraint and its fluctuations are considered, the situation changes drastically. In this case, V (q) is screened making d-wave superconductivity very robust. In addition, we show that the early proposal for the presence of an unretarded pairing contribution triggered by the spin-exchange interaction J can be discussed in this context.